Apparatus for trimless sample cup used in X-ray spectroscopy

ABSTRACT

A sample receptacle for retaining a sample that is to be subjected to spectrochemical analysis. The sample receptacle includes a tubular body having at least one open end and a tapered exterior wall. A sheet of thin film material having peripheral edges is disposed across the open end of the tubular body. A generally annular collar, having an interior wall tapered at an angle supplemental to the taper of the interior wall, is disposed around the tubular body. As the annular collar is placed around the tubular body, the tapered exterior wall of the tubular body creates an interference fit with the tapered interior wall of the annular collar. The tapered surfaces of the tubular body and the annular collar engage the sheet of thin film material and pull the sheet of thin film material taut over the open end of the tubular body. The annular collar is sized to engage the entire length of the exterior wall of the tubular body. The portions of thin film material not covering the open end of the tubular body, including the peripheral edges of the thin film material are compressed between the tapered exterior wall of the tubular body and the tapered inside wall of the annular collar. As such, the sample receptacle can be handled without having to trim extraneous thin film material from the sides of the tubular body.

This is a continuation of application Ser. No. 08/010,555, filed Jan.28, 1993 entitled Method and Apparatus for Trimless Sample Cup Used inX-Ray Spectroscopy now abandoned.

FIELD OF THE INVENTION

This invention relates to a sample cup for use in holding specimens forspectrochemical analysis, and more particularly to a sample cupcomprised of a collar that pulls a thin film material taut over the openend of cell body, thereby obstructing one end of the cell body andcreating the sample cup. The collar engages the thin film material in amanner that eliminates the need to trim the thin film material, therebyincreasing the efficiency by which sample cups can be prepared.

BACKGROUND OF THE INVENTION

Spectroscopy is the science where a sample substance is analyzed bymeans of the spectra of light the sample absorbs or emits. Technologicaladvancements in both wavelength-dispersive (WD-XRF) andenergy-dispersive (ED-XRF) X-ray fluorescence instrumentation enable thespectroscopic analysis of virtually all types of sample materials. Inthis technology, sample cups or sample receptacles are employed to holdor contain liquid, solid and powdered specimens. Many conventional priorart sample cups consist of four components. The four components includea cell body with at least one open end; a thin film of material capableof covering the open end of the cell body; an annular collar used topull the thin film of material taut over the open end of the cell body;and a snap-on ring used to secure the thin film of material in place.The thin film of material encloses a sample substance within the cellbody and provides a sample surface plane which is exposed to anexcitation source, such as an X-ray tube, during the spectrochemicalanalysis. Such conventional prior art cups are exemplified by U.S. Pat.No. Des. 238,693 entitled "CELL FOR X-RAY SPECTROSCOPY OR SIMILARARTICLE" issued on Feb. 3, 1976 to Monte J. Solazzi; U.S. Pat. No.4,409,854 entitled "SAMPLE CUP WITH VENTING MEANS FOR USE IN X-RAYSPECTROSCOPY" issued on Oct. 18, 1983 to Michael C. Solazzi; U.S. Pat.No. 4,643,033 entitled "SAMPLE CUP FOR USE IN X-RAY SPECTROSCOPY" issuedon Feb. 17, 1987 to Monte J. Solazzi; U.S. Pat. No. 4,665,759 entitled"SAMPLE CUP WITH A CANTILEVER BEAM VENTING MEANS" issued on May 19, 1987to Monte J. Solazzi; and U.S. Pat. No. 4,698,210 entitled "SAMPLE CUPAPPARATUS FOR USE IN X-RAY SPECTROSCOPY EMPLOYING SELECTIVELY OPERATEDVENTING MEANS" issued on Oct. 6, 1987 to Michael C. Solazzi. All of theabove patents are assigned to Chemplex Industries, the assignee herein.

During spectrochemical analysis it is essential for the surface of thinfilm material, which covers the opened top of the cell body, to remainplanar in order to produce reliable dam. The area of the thin filmmaterial that covers the top of the cell body, is known as the samplesurface plane. During the spectrochemical analysis of certain specimensthat exhibit a high abrogation in air, the sample cup retaining thespecimen may be placed within a vacuum or inert gas environment. Underconditions where pressure equalization is not implemented, the thin filmof material covering the sample will distend or bow outwardly due to thedifferential in pressures between the area within the sample cup and theenvironment surrounding the sample cup. This places portions of the thinfilm of material closer to the source of excitation. This variation indistance from the sample plane to the source of excitation alters theintensity of the characteristic radiation of the specimen and alsoalters the intensity of radiation impinging upon the sample specimenfrom the excitation source. Consequently, the spectrochemical analysismay produce erroneous quantitative data. For applications in a gaseousenvironment where pressure is greater on the outside of the sample cupthan within the sample cup, the thin film of material distends or isdrawn into the hollow of the sample cup providing a concave samplesurface. This effect increases the distance between the sample plane andthe excitation source and results in erroneous analytical data.

In order to equalize pressure and eliminate distension of the samplesurface plane, some sample cups are provided with a venting means. Theventing means may be activated to provide pressure equalization betweenthe inside and outside of the cup. Other sample cup designs include amain cell component with both ends opened. This double open-ended cupallows for attachment of the thin film sheet prior to the introductionof the sample. This design is useful for applications in an environmentwhere continuous venting is desired from the moment of sampleintroduction.

In the prior art, when a sheet of the thin film material is positionedover the open end of a cell body by means of the annular collar,portions of the thin film of material extend beyond the collar along theouter walls of the cell body. This excess portion of the thin film ofmaterial has a tendency to flare away from the sides of the cell bodyand impairs the handling of the sample cup. As such, the excess thinfilm material must be trimmed from the sides of the cell body in orderthat the sample cup may be conveniently handled.

Furthermore, in the prior art, securing the thin film of material overthe open end of the cell body is a two step process. First, the annularring must be placed over the thin film of material so as to pull thethin film of material down along the sides of the cell body. Second, thesnap-on ring must be applied to secure the thin film of material intoplace. The two step operation causes excessive manipulation of the thinfilm of material which often results in the ripping of the thin film ofmaterial as the thin film of material is repeatedly stressed against thecell body.

It is therefore an object of the present invention to provide animproved sample cup including a single piece snap-on collar designed toretain a thin film of material over the open end of a cell body, withouthaving any portion of the thin film material extend beyond the snap-oncollar. Such a design eliminates the need to trim extraneous thin filmmaterial from around the cell body. This simplifies sample cuppreparation by reducing operational steps and labor required to assemblethe sample cups.

It is also an object of the present invention to provide a sample cupwhich eliminates wrinkles in the thin film of material which covers theopened end of the cell body. The wrinkle-free thin film of materialprovides a consistently planar sample surface. Specially designed edgeson the cell body prevent inadvertent tearing of the thin film samplesupport material during its attachment.

SUMMARY OF THE INVENTION

The present invention is a sample receptacle for retaining a sample thatis to be subjected to spectrochemical analysis. The present inventionsample receptacle includes a tubular body having at least one open endand a tapered exterior wall. A sheet of thin film material havingperipheral edges is disposed across the open end of the tubular body. Agenerally annular collar, having an interior wall tapered at an anglesupplemental to the taper of the interior wall, is disposed around thetubular body. As the annular collar is placed around the tubular body,the tapered exterior wall of the tubular body creates an interferencefit with the tapered interior wall of the annular collar. The taperedsurfaces of the tubular body and the annular collar engage the sheet ofthin film material and pull the sheet of thin film material taut overthe open end of the tubular body. The annular collar is sized to engagethe entire length of the exterior wall of the tubular body. The portionsof thin film material not covering the open end of the tubular body,including the peripheral edges of the thin film material, are compressedbetween the tapered exterior wall of the tubular body and the taperedinside wall of the annular collar. As such, the sample receptacle can behandled without having to trim extraneous thin film material from thesides of the tubular body.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference is madeto the following description of exemplary embodiments thereof,considered in conjunction with the accompanying drawings, in which:

FIG. 1 is an exploded perspective view of a first exemplary embodimentof a sample cup according to the present invention;

FIG. 2 is a cross-sectional view of the exemplary sample cup embodimentof FIG. 1 shown in a partially assembled configuration;

FIG. 3 is a cross-sectional view of the exemplary sample cup embodimentof FIGS. 1 and 2 shown in an assembled configuration;

FIG. 4 is an exploded cross-sectional view of an alternate embodiment ofthe present invention sample cup; and

FIG. 5 is a cross-sectional view of the alternate embodiment of FIG. 4,shown in an assembled configuration.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, there is shown one preferred embodiment of a samplecup or receptacle 10 according to the present invention. The sample cup10 consists of three members, that include a main cell body 12, a thinfilm material 16 and an annular collar 14 designed to secure the sheetof thin film material 16 over the cell body 12.

The cell body 12 includes a sample retaining region 21 and a reservoirregion 23. The sample retaining region 21 of the cell body 12 is tubularin shape having an open end 22 and a closed end 20. The inner wall 25 ofthe sample retaining region 21 is generally cylindrical and extends inthe vertical direction from the closed end 20 up to the open end 22. Assuch, the inner wall 25 defines a hollow 18, capable of retaining asample specimen (not shown). The outside wall 26 of the sample retainingregion 21 is tapered at an angle of inclination A. The outside wall 26tapers toward the end 22 of the sample retaining region 21. As such, theoutside wall 26 has a first diameter D1 at the open end 22 that issmaller than the second diameter D2 at the closed end 20 of the sampleretaining region 21. The edge 28 of the outside wall 26, proximate theopen end 22, is rounded. Furthermore, a continuous semicircular groove30 is disposed in the outside wall 26 proximate the edge 28.

The taper of the outside wall 26 ends at the interface of the sampleretaining region 21 and the reservoir region 23. The reservoir region 23is comprised of a cylindrical wall 32, having a vertical inside andoutside surface, that surrounds and extends below the closed end 20 ofthe sample retaining region 21. A venting provision 38 may be disposedwithin the closed end 20. The venting provision 38 may be optionallyruptured, thereby allowing the hollow 18 of the sample retaining region21 to communicate with the reservoir region 23. As such, any samplecontained within the sample retaining region 21 can be vented to thereservoir region 23 as is currently practiced in many sample cups of theprior art.

A sheet of thin film material 16 is positioned over the open end 22 ofthe cell body 12. The thin film material 16 is flexible and transparentto the radiant energy used in the spectrochemical analysis. The possiblecompositions of such thin film materials 16 are well known in the artand need not be set forth herein at length.

An annular collar 14 is used to properly position the thin film material16 across the open end 22 of the cell body 12. In the preferredembodiment, the annular collar 14 has a vertical height H that is atleast as high as the sample retaining region 21 on the cell body 12. Theannular collar 14 is generally tubular having first open end 45 andsecond open end 47. The annular collar 14 has an interior wall 42 whichis tapered at an angle of inclination B that is supplementary to theangle of inclination A on the outside wall 26 of the sample retainingregion 21 of the cell body 12. The interior wall 42 tapers toward thesecond open end 47. As such, the first inner diameter D3 of the annularcollar 14, proximate the first open end 45, is larger than the secondinner diameter D4, proximate the second open end 47. The interior wall42 has a rounded edge 29 proximate the second open end 47 that faces theinterior of the annular collar 14. A continuous semicircular protrusion44 extends inwardly from the interior wall 42 proximate the first end 45of the annular collar 14. A lip extension 46 is disposed on the exteriorof the annular collar 14. The lip extension 46 facilitates the handlingand the alignment of the overall sample cup 10 when assembled and placedwithin spectroscopic instrumentation.

Referring to FIG. 2, it can be seen that as the annular collar 14 isadvanced over the cell body 12, the thin film material 16 becomespinched between the outside wall 26 of the cell body 12 and the interiorwall 42 of the annular collar 14. As such, as soon as the second openend 47 of the annular collar 14 passes the open end 22 of the cell body12, an interference fit occurs between the annular collar 14, thin filmmaterial 16 and cell body 12. Consequently, the thin film material 16 isimmediately pulled taut across the open end 22 of cell body 12. As theannular collar 14 is further advanced along the cell body 12, the thinfilm material 16 is then pulled taut over the edge 28 of the outsidewall 26 on the cell body 12. The rounded shape of the edge 28 preventsthe thin film material 16 from being torn by the cell body 12.Similarly, as the annular collar 14 is advanced, the thin film material16 is pulled across the edge 29 of the interior wall 42. The roundedshape of the edge 29 prevents the thin film material 16 from being tornby the annular collar 14.

As the annular collar 14 is advanced along the cell body 12, theinterference fit between the interior wall 42 of the annular collar 14,the thin film material 16 and the outside wall 26 of the cell body 12increases due to the tapered shapes of both the interior wall 42 and theoutside wall 26. As the forces of the interference fit increase, thetautness applied to the thin film material 16 increases, therebyeliminating any folds or wrinkles in the portion of the thin filmmaterial 16 covering the open end 22 of the cell body 12.

Referring to FIG. 3, it can be seen that the annular collar 14completely engages the entire length of the sample retaining region 2 1of the cell body 12 when the sample cup 10 is fully assembled. Assemblyof the sample cup 10 is completed once the annular collar 14 is advancedfar enough over the cell body 12 so that the semicircular protrusion 44on the interior wall 42 of the annular collar 14 fits into thesemicircular groove 30 on the outside wall 26 of the sample retainingregion 21. Completion of assembly is indicated by a characteristic"snap" as the semicircular protrusion 44 coacts with the semicirculargroove 30.

Once the sample cup 10 is assembled, the thin film material 16 is drawntightly over the open end 22 of the cell body 12. The thin film material16 creates a seal over the edge 28 of the cell body 12 which isimpermeable to the sample contained therein. The interference fitbetween the tapered interior wall 42 of the annular collar 14 and thetapered outside wall 26 of the sample retaining region 21 of the cellbody 12 occurs for the entire length of the annular collar 14. Thisprevents any loosening of the thin film material 16 that covers theopened end 22 of cell body 12. As such, the thin film material 16 willremain taut over the open end 22, creating a wrinkle-free sample surfaceplane for the spectrochemical analysis.

As mentioned, the interference fit between the annular collar 14 and thecell body 12 occurs over the entire length of the tapered surfaces. Anythin film material 16 not covering the open end 22 of the cell body 12is compressed between the outside wall 26 of the sample retaining region21 and the interior wall 42 of the annular collar 14. Provided anappropriate length of thin film material 16 is initially used, none ofthe thin film material 16 will extend beyond the length of the annularcollar 14. Thus, the step of having to trim extraneous portions of thinfilm material 16 away from the exterior of the sample cup 10 iseliminated. Use of the sample cup 10 with the one-piece annular collar14 greatly simplifies sample preparation since the number of operationalsteps are reduced.

Any time after the sample cup 10 is assembled, the sample substance maybe subjected to spectrochemical analysis. This will normally requireinverting the sample cup 10 so that the open end 22 of the main cellbody 12 is facing downward. At that time, any substance contained withinthe sample cup 10 will come in contact with the portion of thin filmmaterial 16 covering the open end 22 of the sample retention region 21.The sample is then ready for analysis.

If venting is required during analysis of the sample contained withinthe sample cup 10, the venting provision 38 may be optionally rupturedwith a blunt device for maintaining pressure equalization within thehollow 18 of the sample cup 10 and the X-ray optics environment. Ventingof the sample cup 10 allows the thin film material 16 to maintain aplanar sample surface over the open end 22 of the sample retainingregion 21 by eliminating inward or outward distension under positiveinert gas pressure and in an evacuated condition, respectively. Thereservoir region 23 collects any temperature sensitive fluid samplesubstances having tendencies to expand during analysis.

The main cell component 12 and the annular collar 14 are preferablyfabricated from unrecycled natural polyethylene. This eliminates thepotential possibility of introducing metallic contamination that mayadversely affect the analysis of a sample substance. Polyethylene is oneof a number of thermoplastic materials that can be utilized in thisapplication because of its excellent mass attenuation propertiesencompassing the 1 to 12 Angstrom analyte wavelength range. In addition,polyethylene is resistant to chemical attack, temperature softening, anddegradation from excitation energy sources, as well as exhibitingexcellent tensile strength for adequate sample retention.

Referring to FIG. 4, a second preferred embodiment of a sample cup 50according to the present invention is shown. The sample cup 50 consistsof three members, and includes a main cell body 52, a thin film material16 and annular collar 54 designed to secure the sheet of thin filmmaterial over the cell body 52. The cell body 52 includes a first openend 56 and a second open end 58. Other than the fact that both ends 56,58 of the cell body are open, the sample cup 50 is identical to thesample cup 10 shown in FIGS. 1-3. Consequently, the annular collar 54fits over the cell body 52 to secure the sheet of thin film material 16in the manner previously described.

Referring to FIG. 5, the assembled sample cup 50 is shown with a samplesubstance 60 contained therein. The second open end 58 of the cell body52 remains open even after the sample cup 50 is assembled. As such, thesample substance 60 located within the sample cup is always equalized tothe pressure of the ambient environment. The sample substance 60contacts the portion of thin film material 16 which covers the firstopen end 56 of the cell body 52. Since the pressure within the samplecup 50 is equalized by the second open end 58, the thin film material 16which forms the sample surface, will remain consistently planar. Thesample cup 50 is useful for applications analyzed in an air path orinert gas environment.

It will be understood that the present invention sample cups describedherein are merely exemplary and that a person skilled in the art maymake many variations and modifications to the described embodimentutilizing functionally equivalent components to those described. Assuch, variations and modifications, including differing physicalgeometrics, proportions and materials are intended to be included withinthe scope of the invention as defined in the appended claims.

What is claimed is:
 1. A device for retaining a sample to be analysedspectrochemically, comprising:a first tubular member forming a samplecell, said first tubular member having a first end, a second end, afrustoconically shaped outer surface that converges continuously fromsaid first end to said second end, and an annular flange unitarilyformed with said first end of said first tubular member, said annularflange extending radially away from said outer surface of said firsttubular member and a second tubular member forming a retaining collarused for retaining a thin film to said second end of said first tubularmember, said second tubular member having a first end, a second end, anda frustoconically shaped inner surface which converges continuously fromsaid first end to said second end so that when said first and secondtubular members are assembled together to retain the thin film, saidinner surface of said second tubular member will frictionally engagesaid outer surface of said first tubular member, and said first end ofsaid second tubular member will abut against said annular flange;whereby when said first and second tubular members are initially engagedwith each other to assemble a sample receptacle, said second tubularmember entraps a thin film placed between said inner surface of saidsecond tubular member and said outer surface of said first tubularmember and as said second tubular member becomes fully engaged with saidfirst tubular member, said inner surface of the second tubular membergrasps an overhanging portion of the thin film and progressivelyincreases the tautness of a portion of the thin film which extendsacross the second end of the first tubular member.
 2. The deviceaccording to claim 1, wherein said first end of said first tubularmember is provided with an endwall, said endwall defining a centrallydisposed reduced thickness region which is pierceable to permitatmospheric venting of said sealed sample receptacle.
 3. The deviceaccording to claim 2, further comprising a substantially cylindricalwall extending from said annular flange, said end wall and saidsubstantially cylindrical wall defining a reservoir for containing heatsensitive liquid samples.
 4. The device according to claim 1, whereinsaid second tubular member includes a circumferentially extending beadprojecting from said inner surface adjacent said second end thereofwhich coacts with a circumferentially extending recess in said outersurface of said first tubular member adjacent said second end thereof,said bead engaging said recess when said first and second tubularmembers are fully assembled.